I assume you're using a Tour 9630 as you're in the Tour boards, right? If so, you should change your device information settings through the "my account" link above in the forums. That way, individuals here can help you more effectively should you have futures issues and can see the latest and greatest device you're using!

Regarding your question, were the pictures in question seen in "full screen" before the same ones that are "small" now? Often pictures will appear smaller in BBM when the user who's assigning themselves the photograph zooms-in and crops the photo. When this is done, the bbm profile picture will often appear as a small square instead of a larger, full screen image.

I have this problem with BBM avatars that are synced from the Facebook application. They're about the same size as the finger nail on my pinky finger. It was never like that on my 8330, but it has been like this on my 9630 and 9700. I've never been able to figure it out. Regular avatars (not synced from Facebook) are normal size.